Are you going to use the barrel for food?

I have water in them. I tried latex enamel and spray plastic paint. They both scratch off easily. I will probably just use water based latex and live with scratches.

Annie Sloan Chalk Paint. If you're in the US, it's pricey and not always easy to find, but it will stick to ANYTHING and works just fine outside. Google to find a stockist.

I used those to make cat houses once, I spray painted them with the krylon fusion paint, and it held up great. It covered well, too, since they were bright blue and I painted them a light beige without much effort. They DO make it in a brush on formula now, but I have not tried it, but here's the link: http://www.krylon.com/products/fusion-for-plastic-brushon/

(forgive my typos....tablet wont allow me to move back down into post to edit)

'Fusion for plastic' spray is great!! Light coats, many times is the trick.

Not sure if it was Fusion, but learned something new last time I sprayed. Instructions said to repaint after 1/2 hr (or 20 mins....don't remember) ....OR.....u had to wait a long,long time (again, don't remember...sorry) for 2nd coat.

Point is -- I thought waiting like an hour between coats wad god, but turns out was bad.....that u either do it soon after or wait really long time.

Maybe othets knew this, but it was news to me... :)